Transfer devices of this type are used in machines for blow-molding containers, in which the container is obtained by blow-molding, in a blow mold, a hot preform previously manufactured by injection molding. Such blow-molding machines are used in particular for manufacturing polyethylene terephthalate (PET) bottles.
The perform, which is commonly in the form of a tube, one end of which is closed and the other end of which already has the final form of the neck of the container, is conveyed into the mold after having been heated to an appropriate temperature in a thermal processing oven. Once it has been blow-molded, each container is removed from the mold in order to be sent to the output from the machine.
In general, in the context of producing containers at a high production rate, the blow-molding machines are of the rotary type with a carousel that turns continuously about an axis and which bears on its periphery a series of identical molds.
Conveying devices or transfer devices with a transfer arm thus allow preforms to be introduced into the molds, on the one hand, and the finished containers to be withdrawn, on the other, without having to stop the carousel.
Such transfer devices are described and shown for example in documents FR 2,867,171 and FR 2,802,191, both of which are in the name of the Applicant.
On another hand, in a manner often implemented in plants produced by the Applicant, the molding devices for blow-molding or stretch-blow-molding thermoplastic containers, such as preforms, comprise at least one three-part mold (for example of the type named “jackknife opening”), namely two half molds for the body of the container and a mold bottom for the base of the container, the two half molds being arranged such that they can be displaced with respect to each other between an open position and a closed position, the lower parts of the two half molds and the upper part of the mold bottom having mutually interlocking means in the closed position of the mold in order to lock them together.
Providing a mold with only two half molds is possible when the container to be manufactured has a base with a relatively simple shape and can easily be extracted from the mold by a transfer device as mentioned hereinabove. This is the case in particular when the base of the container has no pronounced reliefs (for example a hemispherical base or flat base).
However, when the base has a complex form (for example a petaloid base or dome-shaped base with an inwardly directed convexity), the mold bottom part encloses and traps the base of the formed container and the latter cannot be extracted from the mold, without touching this mold bottom part, if using transfer devices as are currently employed. In other words, the container cannot be extracted from a two-part mold without being deformed and therefore damaged.
In order to remedy this problem, and as is described in document FR 2,841,495 in the name of the Applicant, three-part molds with an axially displaceable mold bottom are used to manufacture containers having a base with a complex shape.
However, in order to produce an axially displaceable mold bottom, it is necessary to provide displacement means for displacing this mold bottom synchronously with the opening and closing movements of the two half molds, this being relatively complex to implement and cumbersome.